Think You're Pretty Smart, Do Ya? Try Baking This Radish Pie, Sucker

A FiveThirtyEight columnist shares a truly tasty puzzle.

I'm what they refer to in the business as a "puzzle head." Big crossword gal. Nuts for a Sudoku. Pretty cool, I know. That's why I enjoy The Riddler, a recurring FiveThirtyEight column by fellow puzzler Zach Wissner-Gross. "Every week, I offer up problems related to the things we hold dear around here: math, logic and probability," Gross writes, explaining that each week's Riddler involves two puzzles: the Riddler Classic, which is a bit of an intensive long solve, and the Riddler Express, which is a quicker challenge. This week's Riddler Express centers on my very favorite thing: pie. Wissner-Gross shares the following puzzle:


"I recently came across a rather peculiar recipe for something called Babylonian radish pie. Intrigued, I began to follow the directions, which said I could start with any number of cups of flour.

Any number? I mean, I had to start with some flour, so zero cups wasn't an option. But according to the recipe, any positive value was fair game. Next, I needed a second amount of flour that was 3 divided by my original number. For example, if I had started with two cups of flour, then the recipe told me I now needed 3 divided by 2, or 1.5, cups at this point.

I was then instructed to combine these amounts of flour and discard half. Apparently, this was my new starting amount of flour. I was to repeat the process, combining this amount with 3 divided by it and then discarding half.

The recipe told me to keep doing this, over and over. Eventually, I'd have the proper number of cups of flour for my radish pie. How many cups of flour does the recipe ultimately call for?"


Readers, this is a tough one. Wissner-Gross does ask that, per Riddler etiquette, you refrain from publicly sharing your answer until Monday. That gives you the whole weekend to mull it over. Well, friends: can you bake the radish pie?